Despite biologic plausibility and widespread enthusiasm, the American Institute of Medicine (IOM) committee found that the evidence that vitamin D reduces cancer incidence and related mortality was inconsistent and inconclusive as to causality. Indeed, for instance 3 vitamin D trials, including one trial comparing a combination of vitamin D with calcium to calcium alone, have assessed the occurrence of newly diagnosed cancers or cancer mortality as secondary outcomes, but the results were null. New trials assessing moderate-to-high-dose vitamin D supplementation for cancer prevention are in progress and should provide additional information within 5 to 6 years. Although future research may demonstrate clear benefits of vitamin D related to cancer and other nonskeletal health outcomes, and possibly support higher intake requirements, the existing evidence falls short.